Bought some battery trays..Questions on install..

[mrbojang 8]

So I just received two of these:

Trans Dapt Performance Products - Battery Trays

Going to install them tonight however I'm wondering what those clips and second piece is?

Also, I'm going to drill into the rear cargo area of my tahoe and bolt those trays down...How do I ensure I'm not drilling into something important? (On the bottom of the truck)

Thanks

[mrbojang 8]

So I went under my truck to inspect what's near where I wanted to drill...Turns out the gas tank is right there. :| I found another place to locate them..

Still no idea what those clip looking things are for? I assume something to do with the hold down? Any ideas?

[Kanaworm$ 292]

How much were those?

The clips look to attach to the tray to tighten the top? ...

[mrbojang 8]

How much were those?

The clips look to attach to the tray to tighten the top? ...

Amazon.com: Trans-Dapt 9323 Stainless Battery Tray: Automotive

$50 on amazon..I'm going to call them tomorrow and figure out wtf to do with those side pieces. I went out and bought some j-style hold down rods...

I'm thinking of using bolts + washers + nuts to secure them down..Self tapping screws would be easier, but they wouldn't be as secure..Right? Kind of clueless on this.